Older adults are disproportionately affected by swallowing impairment, or dysphagia, a condition that can lead to increased morbidity and death. Delayed initiation of swallowing is a common and devastating pathophysiology of neurogenic dysphagia, and is also experienced by healthy older adults, making functional swallowing less safe. Previously we have shown that healthy older adults have significantly delayed swallowing onset as well as increased neural activation in the primary sensory-motor cortex (SMI), a phenomenon absent in younger adults. However, it is still not known if differences in activation of SMI are responsible for delays in swallowing initiation or its consequence with advancing age. The goals of this proposal are;(1) to understand the functional role of SMI on swallowing initiation;(2) to characterize the effect of aging on swallowing initiation with transient cortical disruption;and, (3) for Dr. Humbert to obtain specialized training in neuroscience, sensory-motor control, and aging swallowing physiology. The overall hypothesis is that transient disruption of SMI will produce measurable delays in swallowing initiation in young and old adults, but older adults will have more pronounced deficits. We will apply single-pulse transcranial magnetic stimulation (TMS) to the bilateral SMI laryngeal representation with concurrent video fluoroscopy and electromyography (EMG) during swallowing at various temporal intervals to examine changes in swallowing onset in healthy young and old adults. This investigation will determine whether cortical areas are involved in initiating swallowing as well as the importance of timing on this function. We will also be able to determine whether older adults have a decreased ability to counteract the disruptions to SMI by testing young and old adults. The results from this proposed investigation is significant because the geriatric population is more prone to developing dysphagia due to neurological impairment such as Alzheimer's disease, stroke, and Parkinson's disease. The knowledge gained in this study will become the foundation to develop scientifically sound strategies to reduce this common health care problem that burdens our society. RELEVANCE (See instructions): This investigation is relevant to public health because it will determine whether older adults have a decreased ability to counteract disruptions to the brain, causing delays in swallowing. This is significant because the geriatric population is more likely to develop swallowing impairment due to Alzheimer's disease, stroke, and Parkinson's disease. The knowledge gained in this study will help to develop interventions to reduce this common health care problem that burdens our society.